JP2006156585A - Submount and electronic device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a submount capable of obtaining a good transmission characteristic of a high frequency signal and a heat shielding characteristic.
A high-frequency line conductor is attached to one main surface of a rectangular insulating substrate, and a connection portion connected to an external electronic element on one end side of the insulating substrate is formed on the upper surface of the line conductor. In a submount in which a mounting portion on which an internal electronic element that exchanges signals with an external electronic element is mounted on the other end side than the connection portion is provided directly below the connection portion via at least one side surface of the insulating substrate 1. A notch 4 is formed to communicate with the outside air.
[Selection] Figure 1

Description

  The present invention relates to a submount for mounting an electronic element such as a semiconductor laser element (LD: laser diode) typified by a surface emitting semiconductor laser used in the field of optical communication and the like, and an electronic apparatus using the submount.

  Conventionally, in the optical communication field, an optical semiconductor device has been used to convert a transmitted electrical signal into an optical signal and transmit it to an optical fiber or the like. Such optical semiconductor devices having a data communication bit rate of 2.5 G (giga) bits / second (2.5 Gbps) or higher are widely used. A cross-sectional view of such an optical semiconductor device is shown in FIG. FIG. 4 is a perspective view of a conventional submount mounted on the optical semiconductor device. FIG. 5 is a partial perspective view of the optical semiconductor device.

  An optical semiconductor element housing package (hereinafter also referred to as an optical semiconductor package) 102 constituting the optical semiconductor device 101 is mainly composed of a base body 105, a frame body 109, and a lid body 110. The optical semiconductor package 102 The optical semiconductor element 103 and the like are housed inside, and the optical fiber 108 and the like are attached to the side surface of the frame 109, whereby the optical semiconductor device 101 is obtained.

  A conventional submount 104 will be described below with reference to FIG. 3, and an optical semiconductor device 101 on which the submount is mounted will be described with reference to FIGS.

  A submount 104 and the like are placed on a mounting portion 105 a located at the center of the upper surface of the base 105 via a TEC (thermoelectric cooler) 106. The optical semiconductor element 103 is mounted on the element mounting portion 104a on the upper surface of the submount 104. Further, on the light emitting surface side of the optical semiconductor element 103, a lens 107 for condensing the emitted light onto the optical fiber 108 is placed on the TEC.

  In addition, a frame body 109 is attached to the outer peripheral portion of the upper surface of the base body 105 via a brazing material or an adhesive so as to surround the mounting portion 105a. Further, the frame 109 has a through hole 109a for inserting the optical fiber 108 on a side portion where the optical semiconductor element 103 faces through the lens 107. The optical fiber 108 is inserted into the through hole 109a. A cylindrical fixing member 111 for fixing is inserted.

  In addition, each electrode of the optical semiconductor element 103 is connected to a line conductor of the ceramic terminal 121 provided on the side portion of the frame 109 via a bonding wire, and each electrode of the optical semiconductor element 103 is electrically connected to an external lead terminal. Connect. In particular, a high-frequency line conductor through which a high-frequency signal for E / O (electrical signal-optical signal) conversion is transmitted to the optical semiconductor element 103 is connected to a connector terminal 122 provided on the side of the frame 109 via a connection substrate 123 or the like. May be electrically connected. Then, the lid body 110 is attached to the upper surface of the frame body 109 via a brazing material or an adhesive, and the optical semiconductor element 103 is accommodated inside the container composed of the base body 105, the frame body 109, and the lid body 110. Then, a flange (not shown) attached to the end of the optical fiber 108 is joined to the fixing member 111 by laser welding, and the optical fiber 108 is fixed to the frame 109, whereby the optical semiconductor device 101 is obtained.

  Such an optical semiconductor device 101 excites light to the optical semiconductor element 103 by a drive signal supplied from an external electric circuit via an external lead terminal, and transmits the excited light to the outside via an optical fiber 108. By doing so, it is used for high-speed optical communication. In recent years, such an optical semiconductor device 101 has been increasingly required to have good high-frequency characteristics at 2.5 Gbps or more, miniaturization, low profile, low cost, and the like.

As shown in the perspective view of FIG. 4, the submount 104 is provided with an element mounting portion 104a on the upper surface of the ceramic insulating substrate, and the optical semiconductor element 103 mounted on the element mounting portion 104a is connected to the E / O ( A high frequency signal to be converted is transmitted. The high-frequency line conductor 104b disposed on the upper surface of the submount 104 is connected to the line conductor of the ceramic terminal 121 provided on the side of the frame 109 of the optical semiconductor device 101 or the connector terminal 122 via the connection substrate 123 or the like. Are electrically connected.
Japanese Patent Laid-Open No. 2004-282027

  However, like the above-described optical semiconductor device 101, the line conductor of the ceramic terminal 121 provided on the side portion of the frame body 109, or the high frequency line conductor of the submount 104 after the connector substrate 122 is passed through the connection substrate 123 or the like. When a high-frequency signal of 2.5 Gbps or higher is transmitted to the optical semiconductor element 103 via the 104b, there are the following problems.

  That is, normally, the ceramic terminal 121, the connector terminal 122, the connection substrate 123, and the high-frequency line conductor 104b are designed to ensure impedance matching so as to maintain good high-frequency characteristics because high-frequency signals are transmitted. . However, when the above-described high-frequency signal is transmitted, heat generated from an external electronic element mounted on an external electric circuit serving as a high-frequency signal transmission source is also transmitted to the optical semiconductor element 103 together. For this reason, it is difficult to control the temperature of the optical semiconductor element 103 having a strong temperature dependence, and it is difficult to efficiently convert the transmitted high-frequency electric signal into an optical signal.

  Therefore, in order to block the heat from the external electronic element, it is conceivable to use a ceramic having low thermal conductivity for the ceramic terminal 121. However, the thermal expansion coefficient of the frame 109 of the optical semiconductor element storage package 102 and the low thermal conductivity ceramic is not considered. There is a problem that the alignment cannot be achieved and the airtightness of the optical semiconductor element storage package 102 cannot be ensured.

  It is also possible to use ceramics with low thermal conductivity for the connection substrate 123 interposed between the ceramic terminal 121 or the connector terminal 122 and the submount, but due to the difference in dielectric constant from ceramics such as aluminum nitride forming the submount. Even when impedance matching is performed, it is necessary to extremely narrow or widen the distance between the high-frequency line conductor and the ground conductors on both sides of the high-frequency line conductor and the width of the high-frequency line conductor to form a submount that optimizes high-frequency characteristics. It had the problem that it was difficult.

  The present invention has been completed in view of the problems of the prior art, and an object of the present invention is to provide a submount capable of obtaining good transmission characteristics and high heat shielding characteristics of high-frequency signals of 2.5 Gbps or higher. There is.

  In the submount of the present invention, a high-frequency line conductor is attached to one main surface of a rectangular insulating substrate, and a connection portion connected to an external electronic element on one end side of the insulating substrate is provided on the upper surface of the line conductor. In a submount comprising a mounting portion on which an internal electronic element for exchanging signals with the external electronic element is mounted on the other end side of the connecting portion, at least one end of the insulating substrate is directly below the connecting portion. The notch which leads to outside air through the side surface is provided so as to form a gap in the thickness direction of the insulating substrate.

  The submount of the present invention is preferably characterized in that a conductor layer mainly composed of a metal is deposited on the inner surface of the main surface of the insulating substrate facing the notch.

  In the submount of the present invention, preferably, the conductor layer is electrically connected to a ground terminal.

  In the submount according to the present invention, preferably, the cut is formed in parallel with one main surface of the insulating substrate.

  An electronic device according to the present invention includes the submount according to the present invention mounted on a base, an optical semiconductor element mounted on a mounting portion of the submount, and a lid covering the submount attached. It is characterized by that.

  The submount of the present invention attaches a high-frequency line conductor to one main surface of a rectangular insulating substrate, and connects a connection portion connected to an external electronic element on one end side of the insulating substrate on the upper surface of the line conductor. In a submount comprising a mounting portion on which an internal electronic device for exchanging signals with an external electronic device is mounted on the other end side than the portion, outside air is provided directly below the connection portion via at least one side surface of the insulating substrate. Since the notch leading to the gap is formed so as to form a gap in the thickness direction of the insulating substrate, the surface area of the submount increases, and the heat generated from the external electronic element serving as the high-frequency signal transmission source is increased. Even if it is transmitted to the heat, it becomes possible to efficiently dissipate heat from the surface of the insulating substrate facing the cut. As a result, the temperature control of the optical semiconductor element is facilitated, and the transmitted high-frequency electrical signal can be efficiently converted into an optical signal.

  Further, since heat generated in the external electronic element can be efficiently dissipated in this way, it is not necessary to use ceramics having low thermal conductivity for the ceramic terminal. Therefore, it is possible to avoid the problems that the thermal expansion coefficient of the frame of the optical semiconductor element storage package and the low thermal conductivity ceramic cannot be matched, and the airtightness of the optical semiconductor element storage package cannot be secured.

  Furthermore, since it is not necessary to use ceramics with low thermal conductivity for the connection substrate between the ceramic terminal or connector terminal and the submount, the difference in dielectric constant from the ceramic such as aluminum nitride that forms the submount during impedance matching A submount that optimizes the high-frequency characteristics, eliminating the need to extremely narrow or widen the distance between the high-frequency line conductor and the ground conductors on both sides and the width of the high-frequency line conductor. It becomes possible to form.

  In addition, by changing the width of the cut, the capacitance formed by the line conductor and the lower conductor layer can be easily adjusted. Therefore, even by changing the width of the cut, it is not necessary to extremely narrow or widen the distance between the high-frequency line conductor and the ground conductors on both sides thereof, or the width of the high-frequency line conductor, and the high-frequency characteristics are optimized. Submount can be formed.

  In the submount of the present invention, a conductive layer mainly composed of a metal is applied to the inner surface of the main surface of the insulating substrate facing the notch, so that the metal serves as a heat sink and is better. Can dissipate heat.

  In the submount of the present invention, since the conductor layer is electrically connected to the ground terminal, the conductor layer acts as a ground conductor, and has a capacity between the high-frequency line conductor and the conductor layer. The submount can be mounted on the optical semiconductor device. Because the capacity can be adjusted by changing the distance between the high-frequency line conductor and the ground conductor directly below it, the distance between the high-frequency line conductor and the ground conductor on both sides and the width of the high-frequency line conductor are extremely limited. It is not necessary to narrow or widen.

  In the submount according to the present invention, the notch is formed in parallel with one main surface of the insulating substrate, so that good impedance characteristics can be obtained. This is because the impedance characteristic of the high-frequency line conductor depends not only on the line width but also on the dielectric thickness. For example, when the notch is not parallel to one main surface (upper surface) of the insulating substrate, the thickness of the dielectric The impedance varies depending on the position, and a good impedance characteristic cannot be obtained. However, a good impedance characteristic can be obtained by forming the cut parallel to one main surface.

  An electronic device according to the present invention includes the submount according to the present invention mounted on a base, an optical semiconductor element mounted on a mounting portion of the submount, and a lid covering the submount attached. The heat dissipation of the electronic component is excellent and the operation reliability of the electronic component is high.

  Next, the submount of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a perspective view showing an example of an embodiment of a submount of the present invention. Reference numeral 1 denotes an insulating substrate, 2 denotes an element mounting portion, 3 denotes a high-frequency line conductor, 4 denotes a cut formed on the side surface of the insulating substrate 1, and 5 denotes a conductor layer formed in the cut 4, and these are mainly used in the present invention. A submount is configured. Moreover, each manufacturing process of the submount of this invention is shown to Fig.2 (a)-(f).

The insulating substrate 1 has a function of mounting an optical semiconductor element, and is, for example, a rectangular parallelepiped having a length of about 0.5 to 5 mm, a width of 0.5 to 5 mm, and a height of about 0.5 to 5 mm, and sintered with aluminum oxide (Al ₂ O ₃ ). Body, aluminum nitride (AlN) sintered body, silicon carbide (SiC) sintered body, silicon nitride (Si ₃ N ₄ ) sintered body, ceramics such as glass ceramics, epoxy resin, polyimide resin, polyimide siloxane resin It consists of an insulating material containing resin. In particular, when a material having a thermal conductivity of 40 W / m · K or more, for example, an aluminum nitride sintered body, a silicon carbide sintered body, a silicon nitride sintered body, or the like is used, the heat generated by the optical semiconductor element when it is driven. Is preferably diffused efficiently.

  The insulating substrate 1 has an element mounting part 2 on which an optical semiconductor element is mounted and a high-frequency line conductor 3 electrically connected to the element mounting part 2 on one main surface (upper surface). The element mounting portion 2 has a function of mounting an optical semiconductor element and a function of electrical connection, and the high frequency line conductor 3 has a function of electrically connecting the element mounting portion 2 and an external high frequency line (not shown). Yes.

  Further, the insulating substrate 1 is provided with a notch 4 on the side surface so as to form a gap in the thickness direction of the insulating substrate 1, and the notch 4 increases the surface area of the submount so that a high-frequency signal transmission source can be obtained. Even if the heat generated from the external electronic element is transmitted to the submount, the heat can be efficiently dissipated from the surface of the insulating substrate 1 facing the notch 4. As a result, the temperature control of the optical semiconductor element is facilitated, and the transmitted high-frequency electrical signal can be efficiently converted into an optical signal. Further, since the cut 4 is formed, the capacitance between the high-frequency line conductor 3 and the lower conductor layer formed on the other main surface (lower surface) of the insulating substrate 1 is (1) between the line conductor 3 and the cut 4. (2) the region of the notch 4 and (3) the region between the notch 4 and the lower surface of the insulating substrate 1, and by changing the width of the notch 4, the line conductor 3 and the lower conductor layer The capacity formed by can be easily adjusted. Since the capacity can be adjusted in this way, the high frequency characteristics are optimal without extremely narrowing or widening the distance between the high frequency line conductor 3 and the ground conductors on both sides of the high frequency line conductor 3 or the width of the high frequency line conductor 3. A submount can be formed. In particular, the inner surface of the insulating substrate 1 facing the notch 4 is coated with a conductor layer mainly composed of metal, so that the metal functions as a heat sink, so that heat dissipation is further improved. preferable.

  Further, it is preferable that the conductor layer 5 is electrically connected to the grounding terminal, whereby an optimally sized submount can be obtained. This is because, when the conductor layer 5 is grounded in this way, a capacitive component can be formed between the high-frequency line conductor 3 and the conductor layer 5 that is the ground conductor. The thickness of the insulating substrate 1 below the notch 4 can be freely changed while maintaining good. Therefore, when the thickness of the submount has to be increased due to the structure of the optical semiconductor device, (3) the height of the region between the notch 4 and the lower surface of the insulating substrate 1 can be adjusted, and the optimum size. Submounts can be formed. In addition, it is not necessary to change the distance between the high-frequency line conductor 3 and the ground conductors on both sides of the high-frequency line conductor 3 and the width of the high-frequency line conductor 3, which have been changed for impedance matching, and the radiation electric field strength is stable, Propagation can be done with less noise.

  The electrical connection of the conductor layer 5 to the ground terminal is, for example, by forming a side conductor, a castellation conductor or the like on the side surface of the insulating substrate 1, and This can be implemented by electrically connecting to a ground conductor.

Furthermore, it is preferable that the notch 4 is formed in parallel with one main surface of the insulating substrate 1. This is because the impedance characteristic of the high-frequency line conductor 3 depends not only on the line width but also on the dielectric thickness. For example, when the notch 4 is not parallel to one main surface of the insulating substrate 1, Although the thickness varies depending on the position and a good impedance characteristic cannot be obtained, a good impedance characteristic can be obtained when the cut 4 is formed parallel to the upper surface. In addition, the distance between the notch 4 formed on the side surface of the insulating substrate 1 and parallel to one main surface of the insulating substrate 1 is preferably 0.1 mm or more. If it is smaller than 0.1 mm, there is a possibility that the insulating substrate 1 is broken due to the strength problem. In addition, the distance between the notch 4 parallel to one main surface of the insulating substrate 1 is such that the wavelength λ of the transmitted high frequency signal is improved from the viewpoint of suppressing the resonance in the high frequency region and improving the transmission characteristic of the high frequency signal. A thickness of 1/2 or less is preferable. Note that λ is obtained by c (speed of light) / {f (frequency) × (ε _r (dielectric constant of insulating substrate)) ^1/2 }.

  Details of a method for forming the cuts 4 parallel to one main surface of the insulating substrate 1 will be described later.

  The element mounting portion 2, the high-frequency line conductor 3, and the conductor layer 5 are formed by a conventionally known thin film forming method such as a vapor deposition method, a sputtering method, a CVD method, or a plating method, and a conventionally known photolithography method or etching method. , And processed into a predetermined pattern by a lift-off method or the like.

  The element mounting portion 2, the line conductor 3, and the conductor layer 5 are composed of a conductor layer having a three-layer structure in which an adhesion metal layer, a diffusion prevention layer, and a main conductor layer are sequentially laminated, for example.

From the viewpoint of improving the adhesion with the insulating substrate 1 made of ceramics or the like, such an adhesion metal layer is made of titanium (Ti), chromium (Cr), tantalum (Ta), niobium (Nb), nickel- It is preferably made of at least one kind of metal having a thermal expansion coefficient close to that of ceramics, such as chromium (Ni—Cr) alloy, tantalum nitride (Ta ₂ N), etc., and its thickness is preferably about 0.01 to 0.2 μm. If the thickness of the adhesion metal layer is less than 0.01 μm, it tends to be difficult to firmly adhere the adhesion metal layer to the insulating substrate 1, and if it exceeds 0.2 μm, the adhesion metal layer is insulated by internal stress during film formation. There is a tendency to be easily peeled from the substrate 1.

  In addition, the diffusion prevention layer is made of platinum (Pt), palladium (Pd), rhodium (Rh), nickel (Ni), Ni—Cr alloy, from the viewpoint of preventing mutual diffusion between the adhesion metal layer and the main conductor layer. It is preferably made of at least one metal having good thermal conductivity such as Ti—W alloy, and the thickness is preferably about 0.05 to 1 μm. If the thickness of the diffusion prevention layer is less than 0.05 μm, defects such as pinholes tend to be generated, making it difficult to perform the function as the diffusion prevention layer. If the thickness exceeds 1 μm, the diffusion prevention layer is caused by internal stress during film formation. There is a tendency to easily peel from the adhesion metal layer. Since the Ni—Cr alloy has good adhesion to the insulating substrate 1, it is possible to omit the adhesion metal layer when using the Ni—Cr alloy for the diffusion prevention layer.

  Furthermore, the main conductor layer is preferably made of at least one of gold (Au), Cu, Ni, and silver (Ag) having a low electric resistance from the viewpoint of reducing the electric resistance of the high-frequency line conductor 3. The thickness is preferably about 0.1 to 5 μm. If the thickness of the main conductor layer is less than 0.1 μm, the electric resistance becomes large and it is difficult to satisfy the electric resistance value required for the high-frequency line conductor 3. If the thickness exceeds 5 μm, the main conductor is caused by internal stress during film formation. The layer becomes easy to peel from the diffusion preventing layer. Since Au is expensive, it is preferably formed as thin as possible in terms of cost reduction. Further, since Cu is easily oxidized, a protective layer made of Ni and Au may be coated thereon.

  Next, the manufacturing method of the submount of the present invention will be described with reference to FIG.

  [1] As shown in FIG. 2A, ceramic green sheets 6 made of aluminum nitride are laminated and fired at a temperature of about 1500 ° C. to obtain a ceramic substrate 7 as an insulating substrate 1.

  [2] The main surface of the ceramic substrate 7 is polished with alumina abrasive grains so that the arithmetic average roughness is about 0.1 μm.

  [3] As shown in FIG. 2B, a 0.1 μm thick Ti layer (adhesion metal layer) and a 0.2 μm thick Pd layer are formed on the polished main surface of the ceramic substrate 7 by ion plating. (Diffusion prevention layer) and 0.2 μm thick Au layer (main conductor layer) are sequentially formed, and after patterning by photolithography, a 3 μm thick Au plating layer is deposited on the pattern by electrolytic plating Let Thereafter, the element mounting portion 2 and the high-frequency line conductor 3 are further formed by an etching method.

  [4] As shown in FIG. 2 (c), the ceramic substrate 7 on which the element mounting portion 2 and the high-frequency line conductor 3 are formed is cut into a strip-shaped ceramic strip substrate 8 using a dicer, a slicer or the like.

  [5] As shown in FIG. 2D, the ceramic strip substrate 8 is placed on the cutting device with the surface on which the cut 4 of the surface (side surface) cut in [4] is to be formed as the upper surface, and the same as in [4]. The notch 4 is formed by grinding with a dicer, a slicer or the like.

  [6] As shown in FIG. 2 (e), a 0.1 μm thick Ti layer (adhesive metal layer) and 0.2 μm thick are formed by ion plating on the surface of the ceramic strip substrate 8 where the cuts 4 are formed. A Pt layer (diffusion prevention layer) and a 0.5 μm thick Au layer (main conductor layer) are sequentially formed to form the conductor layer 5 inside the cut.

  [7] As shown in FIG. 2 (f), the ceramic strip substrate 8 which is a mother substrate for taking a large number of pieces is cut by grinding with a dicer, a slicer or the like, and divided into individual submounts.

  In addition, the submount is fired at a temperature of about 1500 ° C after laminating ceramic green sheets made of aluminum nitride ceramic green sheets by die molding or press-molding aluminum nitride powder. Thus, the ceramic strip substrate 8 in which the cuts 4 are formed can also be formed. The ceramic substrate produced by this lamination method or press method is cut and divided into individual pieces by grinding using a slicer after the steps [2], [3], [6] and [7].

  It should be noted that the present invention is not limited to the above-described best embodiment, and various modifications may be made without departing from the scope of the present invention.

It is a perspective view which shows an example of embodiment of the submount of this invention. (A)-(f) is a figure which shows each manufacturing process of the submount of this invention. It is sectional drawing of the electronic device for demonstrating the conventional submount. It is a perspective view of the conventional submount. It is a perspective view of the optical semiconductor device carrying the conventional submount.

Explanation of symbols

1: Insulating substrate 2: Element mounting portion 3: High-frequency line conductor 4: Cut 5: Conductor layer

Claims (5)

A high-frequency line conductor is attached to one main surface of the rectangular insulating substrate, and a connection portion connected to an external electronic element on one end side of the insulating substrate on the upper surface of the line conductor is different from the connection portion. In a submount comprising a mounting portion on which an internal electronic device for exchanging signals with the external electronic device is mounted on the end side, it is exposed directly to the outside via at least one side surface of the insulating substrate immediately below the connection portion. A submount characterized in that a notch that communicates is provided so as to form a gap in the thickness direction of the insulating substrate. The submount according to claim 1, wherein a conductor layer mainly composed of a metal is attached to an inner surface of the main surface of the insulating substrate facing the notch. The submount according to claim 2, wherein the conductor layer is electrically connected to a ground terminal. The submount according to claim 3, wherein the cut is formed in parallel with one main surface of the insulating substrate. A submount according to any one of claims 1 to 4 is mounted on a base, an optical semiconductor element is mounted on a mounting portion of the submount, and a lid that covers the submount is attached. An electronic device.

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